Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 95

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only a little superficially in the air and when they fall down
they fuse together into a flowing lava in which the “lump
stage” is not or only indistinctly seen. This process I had
opportunity to observe in the 1961 eruption in Askja. But if
the lumps, instead of falling on a glowing lava surface, fall
into water, or if the eruption takes place under water there
is the great difference that the lumps will for obvious rea-
sons generally not fuse together. Thus fragmentation is a nor-
mal stage in such eruptions as we probably have to deal with
and the role of water is to prevent more or less completely
a passing beyond this stage. In more explosive eruptions cool-
ing hy water is of course not necessary for the formation
of fragmental masses.
Several dykes (d) with directions between W 20 °S and W
20°N cut (4), hut whether they cut (5) is not seen. They are
bulbous, indicating intrusion into a soft mass (cf. next sec-
tion).
On (5) rests a 25 m thick layer (6) of horizontally strati-
fied sediments. At the bottom we find mainly small grains
of glass and pumice but soon the content of wom pebbles
of various basalt types as well as of older brown tuff increases.
The colour is brown-grey. Partly the sediment is very coarse,
containing boulders up to 1—2 m in diameter, and glacially
striated stones are found, although very sparse. The matrix
is always coarse, clay being practically absent. River wom
gravel is also absent. The material is probably weathering
debris transported by meltwater floods rather than by gla-
ciers. The sediment is mostly very hard. The topmost layer
of (6) is a primary breccia. This is covered by the basalt
lavas (7) which form a part of the topmost lava series of
the mountain (7a). After erosion these lavas were covered by
eolian light-brown tuff (8) containing small worn pebbles.
A dyke (W 50°N) cuts the tuff.
Now a steep, in part very steep slope was formed. It is seen
cutting directly (4), (5), and (6). On this slope was deposit-
ed a stratified mass (9) of bomhs and bomb fragments with